The image we have of St. Francis as the happy, holy troubadour of God from the Franco Zeffirelli movie “Brother Sun, Sister Moon” isn’t quite true to the historical Francis, said Father Augustine Thompson, OP, Ph.D., author of a new and acclaimed biography called “Francis of Assisi” (Cornell University Press, 2012).

Over the years, the stories about Francis have made him seem perfect, said Father Augustine. People “put things into his mouth — things he never said — and they have become conventional wisdom.

“If you filter those out,” he continued, “you see he goes through dark nights of the soul, when he was feeling inadequate. [He is] not the birdbath saint.”

Father Augustine spent several years researching the historical Francis.

“For the first time in 25 years as a practicing historian, I got to do what historians always dream of doing: Be a detective. Especially for medievalists, it’s very rare you have a bunch of evidence like a detective has and you get to put together what lies behind the evidence.

“I had a pile of carefully prepared evidence so I could sit down and try and figure out what I thought happened,” he said. “It was really like being Agatha Christie.”

In his work, Father Augustine uncovered several little-known facts, as well as numerous misconceptions, about Francis. Some of these include:

1. Francis’ father wasn’t a wicked, hateful man.

Pietro de Bernardone, his wife Pica and their other son, Angelo, weren’t villains. Thompson explains that in the earliest accounts of their relationship, the family didn’t realize they had a saint in their midst and were confused and hurt by his actions. Originally, his father is presented as someone who suffered because he didn’t understand his son. However, shortly after Francis’ death, the relationship was rewritten so that his father became a totally evil money- grubber, probably to highlight Francis’ radical decisions.

2. Francis’ great conversion didn’t happen when he stripped naked and renounced his family fortune.

The iconic scene with the bishop had more to do with inheritance law than with holiness, said Father Augustine. It was working among lepers in a leprosarium on the outskirts of Assisi, he said, that “would always be for Francis the core of his religious experience.”

Francis’ “experience with the lepers had nothing to do with choices between wealth and poverty, knightly pride and humility, or even doing service instead of conducting business. It was a dramatic personal orientation that brought forth spiritual fruit.”

3. He probably suffered from post-traumatic stress disorder.

Francis tried his hand at being a soldier when, at age 20, he was part of a military expedition against a neighboring state. He was taken prisoner and spent a year as a captive. The experiences on the battlefield seemed to have marked him for the rest of his life.

“He was a very fragile psyche,” said Father Augustine, “who carried with him a lot of demons.

“He struggled with the horrors of the battles. It looks like post-traumatic stress disorder, and [while I] don’t like doing psychology on someone who lived 800 years ago, he was clearly traumatized by his time in the service.”

4. Francis was not a rebel against the institutional church.

“The one thing people need to remember is Francis was a devout, committed 13th-century Catholic,” said Father Augustine. “If you read modern spiritual writers on Francis, he is always a model for confronting hypocrisy in institutions. My answer to that is a sigh. [The image of] Francis at war with the institutional church is . . . completely anachronistic.”

5. Many of the stories we associate with Francis are legends.

Tales such as the wolf of Gubbio and the talking crucifix were added by early hagiographers, said Father Augustine.

“What a hagiographer does is remodel the story to give a theological message,” he explained. “The job of the hagiographer is not to tell a history. They are to tell you the religious meaning of the person. . . . One of the things they do is tell us that this person is a saint, so they conform the person to the canons of what an age thinks a saint should be like.”

6. Francis didn’t write the “Peace Prayer of St. Francis.”

“I have often been astonished at how unhappy students can be when they encounter a different Francis from the one they expect. Oddly enough, the most painful moment usually comes when they discover that St. Francis did not write the ‘Peace Prayer of Saint Francis.’

“The ‘Peace Prayer’ is modern and anonymous, originally written in French, and dates to about 1912, when it was published in a minor French spiritual magazine, La Clochette,” said Father Augustine.

So after the stories and misconceptions have been stripped away, what is left of Francis for us today?

The essential and radical love of God that Francis embodies.

“When Francis is confronted with unexpected things, he reconciles himself to them and moves forward,” said Father Augustine, “spontaneously seeking to do God’s will.”

It is “his willingness to follow wherever God leads him, even when it’s not something he expected, that kind of spontaneous seeking to do God’s will,” that is the theme of his life.